Automatic ranging and focusing system



United States Patent Inventor Sidney Kml 6131 N. Harding Ave Chicago,Illinois 60645 Appl. No. 726,847

Filed May 6, 1968 Patented Dec. 1, 1970 AUTOMATIC RANGING AND FOCUSINGSYSTEM 5 Claims, 5 Drawing Figs.

U.S. Cl 95/45,

356/4 Int. Cl. G03b 3/00 Field of Search 95/45;

[56] References Cited UNITED STATES PATENTS 3,262,210 7/1966 Shapiro33/46 Primary Examiner-John M. l-ioran Assistant Examiner-Richard L.Moses Patented Dec. 1, 1970 Sheet L of3 FlG.l

Patented Dec. 1, 1970 Sheet Patented Dec. 1, 1970 3,543,566

Shoot 3 of 3 AUTOMATIC RANGING AND FOCUSING SYSTEM This inventionrelates to cameras and other optical systems and more particularlyconcerns a method of automatically focusing a camera or other opticalsystem.

The term camera as used herein includes film and television cameras andin general any lens system which is required to focus an object onto agiven image plane.

The term photographer" as used herein denotes the user of a camera orother lens system which is required to focus an object onto a givenimage plane.

The terms object distance or distance to the object as used hereindenote the distance to the object plane.

The term image distance as used herein denotes the distance to the imageplane.

In the past, cameras with variable focus have required that thephotographer manually adjust the focus. It often happens however thatmanual adjustment of the focus is too slow, with the result that thescene has changed before the correct focus is achieved, or that thephotographer cannot keep in focus an object whose distance is changing.

It is an object of the present invention to provide a means of rapidlyfocusing a camera which is automatic and which, after a preliminaryadjustment, requires no conscious act of focusing by the photographerother than to look at the object to be focused upon.

In accordance with the present invention, the distance to the object atwhich the photographer is looking is determined by automatically andcontinuously measuring the displacement of the photographers eyes fromtheir reference, or straight ahead, position. Means are provided toautomatically adjust the focus of the camera to the correct settingcorresponding to the object distance as thus determined.

Other objects and various additional features and advantages of theinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof taken in conjunction with theattached drawings and the appended claims.

In the drawings:

FIG. I shows the displacement of the pupils of the photographers eyeswhen looking at an object.

FIG. 2 shows the formation of an image by the lens of a camera.

FIG. 3 is a combined view, partly schematic and partly in plan, of theautomatic focusing portion of a camera in accordance with the presentinvention.

FIG. 4 shows the method used in the present invention for framing andscanning an image of the eye of the photographer for the purpose oflocating its center.

FIG. 5 shows the succession of waveform shaping operations which areused in the present invention to locate the center of each eye of thephotographer.

Referring to FIG. I, which shows the photographer's eyes in plan view,the present invention determines the distance d, to the plane l2containing the object 14 to be brought into focus. d is determined bymeasuring the displacements h, and h of the pupils l6, 18 of thephotographer's eyes 20, 22, respectively, from their reference, orstraight ahead, positions.

' Denoting the difference li -h: as Ah, the following relationshipholds:

A h h -h z-l-s 2-8 R R v v a+( Ah/R .2(s/d c0s 0 (2) where 0 is theangle which the line of sight to the object makes with the reference, orstraight ahead direction, and is given by a= cos-mum (3 Since thephotographer will generally center the object of interest in the fieldof view, 0 will be near zero, allowing cos0 in Eq. (2) to be taken asunity with little error. Thus, Eq. (2) may be approximated as A moreaccurate value of d can be obtained by using a more accurate value ofc05 0 in Eq. (2). A useful relationship, for 0 not too large, is

s n (h.+h. /R allowing cos"0 to be calculated from cos 0: (1-sin (9)Substituting the more accurate value of c05 0 obtained from Eq. (6) andEq. (7) into Eq. (2), the distance d, to the object plane is Ah 4 R (8)While Ah is independent of a shift in the position of the photographer,(h,+h is not. A notch 38 in the camera body is provided in which thephotographer places the bridge of his nose, thereby fixing thecoordinate system of his eyes relative to the camera. In an adjustmentprocedure prior to using the camera, a virtual, test image appearing tobe at an infinite distance straight ahead is presented to thephotographer by the present invention. As the photographer looks at thetest image, the reference, or straight ahead, position of each eye isdetermined by a position-measuring device 58 in a manner describedbelow. The reference positions for each eye are stored in the camera.

The interpupillary distance 2: is obtained as the spacing between thetwo reference positions. In subsequent use, the positions It. and h; ofthe photographer's eyes are measured relative to the stored referencepositions. Ah, the change in the interpupillary distance, is equal toh,h

To determine the eyeball radius R, the photographer manually focuses thecamera on a nearby object centered in the field of view, obtaining d,from the calibration of the manual focus adjustment. R, from Eq. (5 isthen obtained as where f is the focal length of the lens. The requiredfocusing adjustment d, is seen from Eq. 10) to vary inversely as theobject distance d Since Ah, from Eq. (2), is also inversely proportionalto d,,, it follows that the required focusing adjustment d, isproportional to the change Ah in the interpupillary distance. CombiningEq. (2) and Eq. (10), the following proportional relationship between d,and Ah is obtained:

d =KAh Referring to FIG. 3, the photographer places the bridge of hisnose in a notch 38 in a shield 45 which causes his eyes to be locatedbehind narrow horizontal slots 42, 44 in said shield. The purpose of theshield is to mask off all portions of the eyes except that behind thehorizontal slots. The photographer's eyes 20, 22 are illuminated bylight 32, 34 from the scene to be photographed and. if greaterillumination is needed, by light sources 36, 40 attached to the camera.Light reflected from the photographer's eyes passes through slots 42,44, is reflected by half-silvered mirrors 46, 48, is imaged onto imagescanners 50, 52, and is detected by photocells 51, 53. The imagescanners scan the image of each eye with a narrow vertical slit 74, andthe photocells convert the light into electrical waveforms 54, 56.Position-measuring devices 58, 60 operate on the electrical waveforms todetermine the displacements h, and I1 of the photographer's eyes. Themeasured displacements h and 11-, are put into the object distancecomputer 62 which computes the distance 11,, to the object planeaccording to the relationship of Eq. (5) or Eq. (8). The computed valueof d is put into the focus setting computer 64 which computes the imagedistance d,- required for proper focus according to Eq. (l). Thecomputed value of d, is applied to a servomechanism 66 or otherproportional control device which mechanically adjusts the cameras focuscontrol 68 to the proper image distance d,-.

Referring to FIG. 4, the framing and scanning of one of thephotographer's eyes 20 is shown. To see the scene to be photographed,the pupil 16 of the photographer's eye is positioned behind a narrowhorizontal slot 42. That portion of the eye behind the slot is imagedonto the image scanner 50 where it is scanned horizontally by a narrowvertical slit 74. The slot 42 is long enough so that the white of theeye 76, the iris 78, and the pupil 16 are all visible through the slot.The light passing through the scanning vertical slit 74 is convertedinto an electrical waveform 54 by a photocell 51.

FIG. shows the electrical waveform 54 resulting from scanning the eye,and an exemplary sequence of wave-shaping operations performed by theposition-measuring device 58 for the purpose of locating the center ofthe eye. The electrical waveform 54 out of the photocell is shown inFIG. 50. It has three distinct levels: the highest level 80 is due tothereflectance of the white of the eye, the intermediate level 82 is dueto the reflectance of the iris, and the lowest level 84 is due to thereflectance of the pupil. The waveform 54 is symmetrical about itscenter because of the symmetry of the eye. The center 86 of the waveform54 corresponds to the time at which the center of the eye is scanned.The position-measuring device 58 locates the center 86 of waveform 54,thereby locating the center of the eye.

In the first step of processing the waveform 54 to locate its center,the portion of the waveform corresponding to the pupil of the eye isremoved by clipping the waveform at a low level 88. The clipped waveform90 is strongly limited at level 92 as shown in FIG. 5b. The limited andamplified waveform 94, shown in H6. 50, is essentially rectangular. Thecenter t of the rectangular waveform 94, corresponding to the center ofthe eye, is determined by averaging the instants of time t, and 1corresponding, respectively, to the rise and fall of the rectangularwaveform 94, or

Returning to FIG. 3, the displacements h, and h,, as determined byposition-measuring devices 58 and 62, are put into the object distancecomputer 62 which calculates the distance d,, to the object according toeither Eq. (5) or Eq. (8). The output d of the object distance computeris put into the focus setting computer 64 which calculates the requiredimage distanced, according to Eq. (l0). lf Eq. (5) is used to determined,,. the relationship between d, and Ah is one of directproportionality, d; [(1311, as given by Eq. (1 l In this case, thecombined task of the object distance computer 62 and the focus settingcomputer 64 is simply to form the difference Ah= h,h, and multiply it bya proportionality factor K. The image distance d, calculated by thefocus setting computer 64 is applied to a servomechanism 66 or otherequivalent means to position the focus control 68 of the camera to theposition corresponding to the required image distance 11 he presentinvention, In its ObJCl distance measuring capacity, may also be usedfor purposes of automatic range finding.

Obviously many other modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood, that within the scope of the appendedclaims, the invention may be practiced otherwise than specificallydescribed.

iclaim:

1. In a camera and other optical systems of the adjustable focus type,the combination of measurement means to determine the displacement ofthe pupils of the photographer's eyes from their reference or straightahead position, first computing means responsive to said measureddisplacements for determining the distance to the object at which thephotographer is looking, second computing means responsive to saidobject distance for determining from the appropriate lens formula theimage distance required to bring said object into focus, and controlmeans for positioning the focus control of the camera to said computedimage distance, whereby the object at which the photographer is lookingis rapidly and automatically brought into focus with no manual actionrequired of the photographer.

2. The system as defined in claim 1 wherein said first and secondcomputing means are combined into a single dornputing means, said singlecomputing means having the function of forming the difference Ah, thechange in the interpupillary distance of the photographers eyes, andmultiplying it by a proportionality factor.

3. The system as defined in claim I wherein said measurement means forlocating the center of each eye comprises, in combination, means forilluminating each eye, means for forming an image of each eye,horizontal slot means for framing a portion of the image of each eyecontaining the pupil, vertical slit means for scanning the portion ofthe image of each eye framed by said horizontal slot means,photoelectric means responsive to the light passing through saidscanning vertical slit and producing an electrical output waveform inresponse thereto, and position-measuring means responsive to saidelectrical output waveform for locating the axis of symmetry of thewaveform, whereby the center of each eye, corresponding to the axis ofsymmetry of said electrical output waveform, is located.

4. ln a camera and other optical systems, the combination of measurementmeans to determine the displacement of the pupils of the photographerseyes from their reference or straight ahead position and computing meansresponsive to said measured displacements for determining the distanceto the object at which the photographer is looking, whereby the range tothe object at which the photographer is looking is rapidly andautomatically determined with no manual action required of thephotographer.

5. The system as defined in claim 4 wherein said measurement means forlocating the center of each eye comprises, in combination. means forilluminating each eye, means for forming an image of each eye,horizontal slot means for framing a portion of the image of each eyecontaining the pupil, vertical slit means for scanning the portion ofthe image of each eye framed by said horizontal slot means,photoelectric means responsive to the light passing through saidscanning vertical slit and producing an electrical output waveform inresponse thereto, and position-measuring means responsive to saidelectrical output waveform for locating the axis of symmetry of thewaveform, whereby the center of each eye, corresponding to the axis ofsymmetry of said electrical output waveform, is located.

